The Final Meal of a Dinosaur: A Sauropod’s Intestines from 100 Million Years Ago Reveal Its Eating Habits

Since scholars discovered the first dinosaur fossils, they have maintained that sauropods, the largest of all, were herbivores. This was supported by logic, knowledge of trophic chains, the shape of their teeth, the length of their necks, and their size and slowness, which would prevent them from chasing other animals. However, there was barely any direct evidence, such as coprolites (fossilized feces) or, even less, cololites (fossilized digestive contents). Until now, when a group of researchers details in the journal Current Biology the finding of a cololite from a young sauropod that lived in what is now northeast Australia. In its stomach, it contained what it had last eaten: a varied diet consisting of conifers, ferns, and leaves from early angiosperms, the flowering plants. Additionally, they noted that it barely chewed its food.

“There has been scientific consensus about the plant-based diet of sauropods for over 150 years. However, definitive intestinal content from a sauropod has never been obtained, hence the significance of our fossil,” explains Stephen Poropat, a researcher at Curtin University (Australia) and lead author of this study, in an email. “This finding confirms several hypotheses about the diet of sauropods that were previously formulated based on studies of their anatomy and comparisons with current animals,” he comments.

Discovered in 2015 a few kilometers from Winton, in the state of Queensland, the sauropod specimen was a young one that measured eleven meters. It was a Diamantinasaurus matildae, a species that lived in Australian lands during the Cretaceous. In this case, it is estimated that it died between 94 and 101 million years ago. When they began extracting the fossil, paleontologists discovered a strange rocky growth in what would be the abdominal area. Spanning an area of 2×1 meters, with a thickness of up to one meter and a volume of 100 liters, it is the first confirmed cololite from a sauropod. Despite the time elapsed, it reveals almost everything about the diet of the largest animals to have ever walked the Earth’s surface.

“Our sauropod retains remains of at least four different types of plants in its intestinal content: araucarias [a genus of conifers], austrosequoia [related to modern sequoias], seed ferns, and angiosperms [flowering plants],” says the Australian researcher. While many current herbivores have specialized in grasses, these had not yet appeared, especially not in that part of the world. The study refines the understanding of the diet further: from the conifers, the most found were bracts, leaves modified to protect the fruit. From the ferns, they found fruit from an extinct species. And from the angiosperms, leaves from several species. In any case, Poropat adds, “the diet of our sauropod is quite varied.”

Thus, they were generalists, foraging at high and low levels, which provides many clues about their environment. As juveniles, sauropods only had access to plants close to the ground, but as they grew, so did their food options. Additionally, the prevalence of small shoots, bracts, and pods in the cololite implies that young Diamantinasaurus fed on the shoots of conifers and seed ferns, which are easier to digest.

The fact that they ate leaves from angiosperms is significant for researchers, as this type of plant had appeared on Earth not long before. In the fossil record, the first flowering plants were found in what is now the Iberian Peninsula around 130 million years ago. By the time they reached the stomach of young D. matildae, Australia was still connected to what would become Antarctica, but both had long since separated from Gondwana. Hence, angiosperms must have taken their time to reach there. “Angiosperms had spread more or less all over the world by 100 million years ago, and in the flora of the Winton Formation [where the cololite was found], they were co-dominant with conifers and seed ferns, which testifies to their success,” notes Poropat. But it also illustrates the adaptability of dinosaurs, who managed to incorporate them into their diet.

Researchers here emphasize that, long before large herbivorous mammals, it was the large dinosaurs that prepared this planet for flowering plants: angiosperms are known for developing physical or chemical defenses against herbivores, for regenerating and reproducing quickly, and, as this Australian researcher points out, “for housing their seeds in fruits that, when consumed and ultimately excreted by herbivores, are widely dispersed in piles of prepared fertilizer (feces).”

The analysis of the plant remains from the cololite provides one last clue about sauropods: the presence of only slightly chewed leaves and practically whole shoots shows that this young dinosaur barely chewed what it ate, leaving the processing and digestion to its intestinal flora. This hypothesis has been posited for a long time because sauropods do not have teeth adapted for chewing: all their teeth are the same and suited for cutting vegetation, not grinding it. “The intestinal content of our sauropod supports this idea because many of the plants present in it can still be identified because they have not been crushed,” concludes Poropat, who also warns that it would be risky to say that all sauropods had diets identical to that of this young dinosaur just before its death.